President Barack Obama addresses the nation from the Cross Hall in the White House in Washington, Wednesday, Sept. 10, 2014. In a major reversal, Obama ordered the United States into a broad military campaign to degrade and ultimately destroy militants in two volatile Middle East nations, authorizing airstrikes inside Syria for the first time, as well as an expansion of strikes in Iraq. (AP Photo/Saul Loeb, Pool)

WASHINGTON (AP) — President Barack Obama in a major reversal ordered the United States into a broad military campaign Wednesday night to “degrade and ultimately destroy” Islamic State militants in two volatile Middle East nations authorizing airstrikes inside Syria for the first time as well as an expansion of strikes in Iraq.

In an address to the nation, Obama also announced he was dispatching nearly 500 more U.S. troops to Iraq to assist that country’s besieged security forces. And he called on Congress to authorize a program to train and arm rebels in Syria who are fighting both the Islamic State group and Syrian President Bashar Assad.

Saudi Arabia, a crucial U.S. ally in the Middle East, offered to host the training missions, part of Obama’s effort to persuade other nations to join with the U.S. in confronting the militants.

“This is not our fight alone,” Obama declared. “American power can make a decisive difference, but we cannot do for Iraqis what they must do for themselves, nor can we take the place of Arab partners in securing their region.”

“Our objective is clear: We will degrade and ultimately destroy ISIL through a comprehensive and sustained counterterrorism strategy.”

The president adamantly ruled out the prospect of putting American troops in combat roles on the ground in Iraq or Syria.

Even so, Obama’s plans amount to a striking shift for a president who rose to political prominence in part because of his early opposition to the Iraq war. While in office, he’s steadfastly sought to wind down American military campaigns in the Middle East and avoid new wars — particularly in Syria, a country where the chaos of a lengthy civil war has given the Islamic State space to thrive and move freely across the border with Iraq.

Speaking on the eve of the anniversary of the Sept. 11, 2001, attacks, Obama’s plans also amounted to an admission that years of American-led war in the Middle East have not quelled the terror threat emanating from the region.

While administration officials have said they are not aware of a credible threat of a potential attack by the militants in the U.S., they say the Islamic State group poses risks to Americans and interests in the region. Officials are also concerned about the prospect that Westerners, including Americans, who have joined the militant group could return to their home countries to launch attacks.

In recent weeks, the militants have released videos depicting the beheading of two American journalists in Syria. The violent images appear to have had an impact on a formerly war-weary public, with multiple polls in recent days showing that the majority of Americans support airstrikes in both Iraq and Syria.

The U.S. began launching limited airstrikes against Islamic State targets in Iraq earlier this summer. But officials said Obama was waiting for Iraq to form a new government — a step it took Tuesday — before broadening the effort.

Officials said strikes in Iraq would now be wide-ranging and extend into Syria. Obama plans to proceed with those actions without seeking new authorization from Congress.

Instead, officials said Obama will act under a use of force authorization Congress passed in the days after 9/11 to give President George W. Bush the ability to go after those who perpetrated the terror attacks. Obama has previously called for that authorization to be repealed, he has also used the measure as a rationale to take strikes against terror targets in Yemen and Somalia.

Officials compared the new U.S. mission in Iraq and Syria to the actions in Yemen and Somalia, campaigns that have gone on for years.

Obama is seeking authorization from Congress for a Pentagon-led effort to train and arm more moderate elements of the Syrian opposition. Ahead of Obama’s remarks, congressional leaders grappled with whether to support that request and if so, how to get such a measure through the fractured legislature before the November elections.

The White House wants Congress to include the authorization in a temporary funding measure they’re expected to vote on before adjourning later this month. Republicans made no commitment to support the request and the House GOP has so far not included the measure in the funding legislation.

A spokesman for Senate Majority Leader Harry Reid said the Nevada Democrat might opt to seek separate legislation to authorize the president’s request.

While the CIA currently runs a small program to arm the rebels, the new program would be more robust. Obama asked Congress earlier this year to approve a $500 million program to expand the effort and put it under Pentagon control, but the request stalled on Capitol Hill.

Some of Obama’s own advisers, including former Secretary of State Hillary Rodham Clinton, pressed him to arm the rebels early in their fight against Syrian President Bashar Assad. But Obama resisted, arguing that there was too much uncertainty about the composition of the rebel forces. He also expressed concern about adding more firepower to an already bloody civil war.

Separately, the White House announced Wednesday that it was providing $25 million in immediate military assistance to the Iraqi government as part of efforts to combat the Islamic State.

In the hours before the president’s remarks, the Treasury Department said that Obama’s strategy would include stepped-up efforts to undermine the Islamic State group’s finances. David Cohen, Treasury’s undersecretary for terrorism and financial intelligence, wrote in a blog post that the U.S. would be working with other countries, especially Gulf states, to cut off the group’s external funding networks and its access to the global financial system.

The U.S. has also been pressing allies in Europe, the Middle East and elsewhere to help with efforts to degrade the terror group.

France’s foreign minister said Wednesday that his country was ready to take part in airstrikes against extremist fighters in Iraq if needed. And the German government announced that it was sending assault rifles, ammunition, anti-tank weapons and armored vehicles to Kurdish forces in Iraq fighting, breaking with Berlin’s previous reluctance to send weapons into conflicts.

Secretary of State John Kerry is traveling to Saudi Arabia and Jordan this week. He first made a stop in Baghdad to meet with Iraq’s new leaders and pledge U.S. support for eliminating the extremist group.